1. Field of the Invention
The present invention relates to a copying machine comprising an automatic document feeder and a sheet feeder for successively conveying the lowermost sheet out of a plurality of sheets stacked on a sheet tray after an original image is copied on one of their surfaces while blowing air on the leading end of the lowermost sheet to separate the lowermost sheet from the remaining sheets.
2. Description of the Related Art
In order to cope with recent higher speed requirements, the so-called stacking feed operation, in which a stacking operation on a sheet tray and a refeeding operation from the sheet tray are simultaneously performed at the time of duplex copying using an automatic document feeder, has been performed in the above described copying machine.
Furthermore, in a sheet feeder in the above described copying machine, the leading ends of a plurality of sheets above the lowermost sheet are raised by blown air to separate the lowermost sheet from the sheets above the lowermost sheet. The above described blown air is basically required only when sheets are fed again.
On the other hand, certain time (which can be considered a loss in time) is required for an air blowing fan to reach a rated state where a predetermined amount of air is obtained after the driving of the air blowing fan is started. At the time of the above described stacking feed operation for achieving higher speed, such a loss of time is not allowed. Therefore, the air blowing fan is continuously driven to obtain a predetermined amount of air immediately when required.
When the air blowing fan is thus continuously driven, however, the blown air may adversely affect the sheets which are being stacked on the sheet tray.
On the other hand, at the time of duplex copying without using the automatic document feeder, an operator turns an original over when the copying on one of the surfaces of the sheets is terminated, followed by copying on the reverse surfaces thereof. Therefore, a predetermined time period is always required from the termination of the copying on one of the surfaces of the sheets to the start of the copying on the reverse surfaces thereof. Consequently, the sheets, each having an original image copied on its one surface, have been stacked on the sheet tray a predetermined time period before the refeeding of the sheets from the sheet tray is started.
In such a case, it is useless to continuously drive the air blowing fan by the same amount of air as the amount of air after the refeeding from the time before the refeeding is started in the same manner as that in the case of the stacking feed. In addition, the blown air exerts an unnecessary adverse effect on the sheets which are being stacked on the sheet tray, which may result in poor stacking of the sheets.